Duration of fracture prevention after zoledronate treatment in women with osteopenia: observational follow-up of a 6-year randomised controlled trial to 10 years

Background We previously identified that zoledronate administered at 18-month intervals reduced fragility fractures by a third in a 6-year trial of women older than 65 years with osteopenia. This extension aims to identify the persistence of these effects. Methods Of the 2000 ambulant, community dwelling, postmenopausal women older than 65 years recruited in Auckland, New Zealand, with T-scores at the total hip or femoral neck in the range –1·0 to –2·5, we invited participants who received four doses of intravenous zoledronate, completed follow-up to year 6 of the core trial, did not have metabolic bone disease (other than osteoporosis), and were not using bone-active drugs into this 4-year observational study extension, during which further treatment was at the discretion of their own doctors. Participants were asked to notify study staff of any new fractures and were telephoned at 7·5 years and 9·0 years to update their health status. Participants were then invited to an onsite visit at 10·0 years. Fractures and other health events were documented at each contact and analysed in all women who entered the extension, and bone mineral density (BMD; analysed in participants without notable use of bone-active medications who attended an onsite visit at 10 years) and turnover markers (measured from fasting morning blood in a random subset of 50 participants) were measured at year 10. Findings Of the 1000 women randomly assigned to receive zoledronate in the core trial, 796 participants were eligible for the extension, of whom 762 (96%) entered the extension between Sept 24, 2015, and Dec 13, 2017. Mean follow-up duration was 4·24 years (SD 0·57, range 0·61–6·55; final follow-up on May 25, 2022). 727 (91%) of participants were assessed at 10 years. 25 women died during the extension, six withdrew for medical reasons, and four were lost to follow-up. 92 women suffered 114 non-vertebral fractures during the extension. Non-vertebral fracture rates increased from a nadir of 15 fractures per 1000 woman-years (95% CI 10–21) in the last 2 years of the core trial to 24 fractures (17–33) in years 6–8 and 42 fractures (32–53) in years 8–10, similar to that in the placebo group in the last 2 years of the core trial. Total hip BMD (relative risk per 0·1 g/cm2 0·73, 95% CI 0·57–0·93; p=0·011) and a previous history of non-vertebral fracture (1·74, 1·12–2·69; p=0·013) at year 6 predicted incident fractures but change in total hip BMD did not. Total hip BMD decreased from 4·2% above study baseline to 0·8% above baseline (p<0·0001) during the extension. Turnover markers were not useful for predicting BMD loss in individuals. Osteonecrosis of the jaw or atypical femoral fractures did not occur in any participants. Interpretation The reduced fracture rates following zoledronate in the core trial were substantially maintained for 1·5–3·5 years after the last zoledronate infusion, but not thereafter. Funding Health Research Council of New Zealand.